Once semiconductor wafers are prepared, a large number of process steps are still necessary to produce desired semiconductor integrated circuits (ICs). In general the steps can be grouped into four areas: Front End Processing, Back End Processing, Test, and Packaging.
Front End Processing refers to the initial steps in the fabrication. In this stage the actual semiconductor devices (e.g., transistors) are created. A typical front end process includes: preparation of the wafer surface, patterning and subsequent implantation of dopants to obtain desired electrical properties, growth or deposition of a gate dielectric, and growth or deposition of insulating materials to isolate neighboring devices.
Once the semiconductor devices have been created they must be interconnected to form the desired electrical circuits. This “Back End Processing” involves depositing various layers of metal and insulating material in the desired pattern. Typically the metal layers consist of aluminum, copper, and the like. The insulating material may include SiO2, low-K materials or interlayer dielectric (ILD), and the like. The various metal layers are interconnected by interconnects, which may include a line portion and a via portion. Vias may be formed by etching holes in the insulating material and depositing metal (e.g., Tungsten) in them. The line portion may be formed by etching trenches in the insulating material and depositing metal in them.
Once the Back End Processing has been completed, the semiconductor devices are subjected to a variety of electrical tests to determine if they function properly. Finally, the wafer is cut into individual die, which are then packaged in packages (e.g., ceramic or plastic packages) with pins or other connectors to other circuits, power sources, and the like.
As noted above, “patterning” occurs in Front End Processing. This patterning may include etching of materials, similar to the via and line etching referenced with regard to the Back End Processing. Generally, etching is a subtractive process in the course of which a solid may be dissolved in liquid chemicals (wet etching) or converted into gaseous compound(s) (dry etching). Etching process may use a plasma mediated process such as by RF (radio frequency) or by microwave power of hundreds kHz (kilohertz) or several GHz (gigahertz). Etching may entail removal of material by exposing the material to a bombardment of ions (e.g., a plasma of reactive gases such as fluorocarbons, oxygen, chlorine, boron trichloride; sometimes with addition of nitrogen, argon, helium and other gases) that dislodge portions of the material from the exposed surface. Other etching processes may include particle beam induced chemical etching technologies such as electron beam etching, ion beam etching, or laser etching. These particle beam etching processes are generally carried out in the presence of an etching gas such as xenon difluoride (XeF2). In short, etching is a key process in semiconductor processing.